From 2b96102f29d2634a69b04cc782236cb12d8e3e56 Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Mon, 2 Oct 2023 08:43:16 -0700
Subject: [3.12] gh-109889: fix compiler's redundant NOP detection to look past
 NOPs with no lineno when looking for the next instruction's lineno
 (GH-109987) (#110048)

gh-109889: fix compiler's redundant NOP detection to look past NOPs with no lineno when looking for the next instruction's lineno (GH-109987)
(cherry picked from commit f580edcc6a4c528020afe46c753db713474acad6)

Co-authored-by: Irit Katriel <1055913+iritkatriel@users.noreply.github.com>
---
 Lib/test/test_compile.py                                     |  5 +++++
 .../2023-09-27-21-35-49.gh-issue-109889.t5hIRT.rst           |  2 ++
 Python/flowgraph.c                                           | 12 +++++++++++-
 3 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Core and Builtins/2023-09-27-21-35-49.gh-issue-109889.t5hIRT.rst

diff --git a/Lib/test/test_compile.py b/Lib/test/test_compile.py
index b75d1c5..42df670 100644
--- a/Lib/test/test_compile.py
+++ b/Lib/test/test_compile.py
@@ -1269,6 +1269,11 @@ class TestSpecifics(unittest.TestCase):
             while x:
                 0 if 1 else 0
 
+    def test_remove_redundant_nop_edge_case(self):
+        # See gh-109889
+        def f():
+            a if (1 if b else c) else d
+
 @requires_debug_ranges()
 class TestSourcePositions(unittest.TestCase):
     # Ensure that compiled code snippets have correct line and column numbers
diff --git a/Misc/NEWS.d/next/Core and Builtins/2023-09-27-21-35-49.gh-issue-109889.t5hIRT.rst b/Misc/NEWS.d/next/Core and Builtins/2023-09-27-21-35-49.gh-issue-109889.t5hIRT.rst
new file mode 100644
index 0000000..8be373f
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2023-09-27-21-35-49.gh-issue-109889.t5hIRT.rst	
@@ -0,0 +1,2 @@
+Fix the compiler's redundant NOP detection algorithm to skip over NOPs with
+no line number when looking for the next instruction's lineno.
diff --git a/Python/flowgraph.c b/Python/flowgraph.c
index f860631..afcae31 100644
--- a/Python/flowgraph.c
+++ b/Python/flowgraph.c
@@ -981,7 +981,17 @@ remove_redundant_nops(basicblock *bb) {
                 }
                 /* or if last instruction in BB and next BB has same line number */
                 if (next) {
-                    if (lineno == next->b_instr[0].i_loc.lineno) {
+                    location next_loc = NO_LOCATION;
+                    for (int next_i=0; next_i < next->b_iused; next_i++) {
+                        cfg_instr *instr = &next->b_instr[next_i];
+                        if (instr->i_opcode == NOP && instr->i_loc.lineno == NO_LOCATION.lineno) {
+                            /* Skip over NOPs without location, they will be removed */
+                            continue;
+                        }
+                        next_loc = instr->i_loc;
+                        break;
+                    }
+                    if (lineno == next_loc.lineno) {
                         continue;
                     }
                 }
-- 
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